Shine is a huge topic in the beauty industry, especially when it comes to hair. Researchers have now narrowed down the criteria that separates the lustrous from the lacklustre.

Their findings on the shiniest hair might have you in for a bit of a surprise!

Can you really measure shine?That's right; you can actually put a number on how shiny your hair is. To determine the shininess of hair, scientists use instruments which measure the amount of light scattered by the surface of the strand. For maximum shine, you need light to be reflected in a single direction. Scattered light going off in a variety of directions dulls the hair's appearance. Scientists at TRI have not only come up with a comprehensive list of factors that affect shine, they have also managed to map it to your origins. Here's how the shine factors stack up:The shiniest hair is thick Thicker hair – specifically speaking here of the thickness or diameter of the strand itself – tends to have the most gleam. Simply put, the larger surface area allows it to reflect more light in one direction, thus giving it more shine. One caveat, though: if your thick strands also have a large, porous medulla (the innermost part of the hair) then the internal structure will scatter light, cutting down on your shine.

The shiniest hair is the darkest The lighter your hair colour is, the more it scatters the light, sending rays bouncing off in all different directions and leaving your hair looking less than lustrous. The higher amount of pigment in darker hair allows it to absorb more light, which in turn allows it to reflect light more consistently, thanks to the granules of melanin that give the hair its colour and act sort of like semiconductors.

The shiniest hair is well-lubricated Hair can reflect light almost like a mirror when a shine spray or oil layer covers its outer scales completely, forming a smooth surface. Don't go overboard, however, because...The shiniest hair has minimal product build up Scientists have repeatedly shown how conditioning shampoos, conditioners and styling products can leave behind dulling deposits on the hair. These small particles create microscopic roughness on the hair's surface. Just as with damaged hair, this unevenness creates different planes, each of them sending light off in a different direction, reducing shine.

The shiniest hair has an even surface

Whether by cosmetic treatments or merely by combing, damage to the hair's surface affects the way it reflects light. The scales of damaged hair lift and get scraped away, leaving the surface rough and uneven. This sends light scattering off in different directions, creating a drab appearance.The shiniest hair varies by curvature When a fibre is curved, it tends to scatter light off in different directions, even if the fibre itself is inherently very glossy. This is why curly hair often has issues with shine.

The shiniest hair is the most asymmetrical We may be conditioned to imagine the shiniest hair as having a “perfect circle” shape, but this is far from the case. Scientists at TRI found that the shiniest hair had the most elliptical or “flattened oval” form. Typically, the straighter your hair is, the more cylindrical your strands will be, with the curliest hair having the most elliptical shape. You might think that hair with a more cylindrical shape would have the shiniest surface, but think about it; all the light that hits the cylinder is going off more or less equally in different directions. This scatters the light all over the place, sapping the hair's lustre. In contrast, if your strand is more asymmetrical, it will have one plane that reflects a lot more light than the others, getting more light going in one single direction. That kind of consistency equals shine.The shiniest hair is a bit of a surpriseScientists at TRI measured different samples of hair in groups based on biogeographical origin, presenting two different sets of shine calculations. The results turn a lot of assumptions on their heads!

First Shine Calculation by TRI.

Second Shine Calculation by TRI

And the most influential shine factor of them all? COLOURLike to play with colour? The hair types with the most gleam in both indices had three major things in common: large diameter, high ellipticity and a deep hue. The researchers think that dark colour is the biggest factor in shine. Note that all the shiniest hair was black – African hair in particular tends to have a very high number of very large melanin granules, allowing it to reflect a lot of light very consistently, generating natural shine. The hair used in the research was straight, with the exception of the African hair; tresses from the tightly-curled category were selected here, though in reality African hair types range from very straight to tightly-curled. While the light-scattering effect that comes from a curved structure can affect the shine of curly hair, it didn't really impact here as the curls were held straight. A few other elements were also key to its shimmering results: the hair in the research was natural, in good condition and product-free. As stated above, damage (from any source) and product buildup are big shine reducers.